1. Field of the Invention
This invention relates to an adaptive proportional-plus-integral control system (adaptive PI control system) using adaptive control, and more particularly, to an adaptive PI control system for controlling a robot, a machine tool which is subject to large load variation or the like.
2. Description of the Related Art
Conventionally, in plants such as robots and the like, systems are generally controlled by a PI control loop having a fixed gain, and parameters of the systems are adjusted manually through trial and error,
For the PI control system such as those used in the robots and the like, it is important to have quick response and robustness for being capable of coping with the variation of the parameters such as the variation of the inertia.
When a servo system is constituted of a conventional PI control system, a large feedback gain will be needed for obtaining quick response of the system, since the control by such a conventional system is solely dependent on the feedback loop. If the feedback gain is too large, however, the stability of the servo system is lost and oscillation is liable to occur. Thus, in the case of a conventional system, the response can be enhanced only to a limited extent. To improve the response while at the same time maintaining the system stability, a control method using a feedforward loop may be employed; however, this method has a drawback such that the control operation is easily affected by a parameter variation in the controlled system due to the absence of the feedback from the controlled system.
Even in the case of a controlled system in which the quick response is not so important, parameter adjustment of the feedback loop so time-consuming that the actual application of this method is very difficult due to the difficulty of setting the parameters to optimum values.